Evidence for New Phase occurring in Portland Cements

Abstract

THE X-ray powder diffraction patterns normally obtained from Portland cements contain only lines which can with confidence be said to be due to the presence of the four major phases, alite (modified C₃S), C₂S, C₃A*, a ferrite phase in the solid solution series C₆A₂F–C₄AF–C₂F and minor constituents such as CaO, MgO and CaSO₄. Recently, however, I have obtained from a few cements diffraction patterns in which a number of unusual lines were present. The new lines, from their position and intensity, appear to be produced by material having a structure closely similar to perovskite, that is, orthorhombic, pseudo-cubic, α′= 3.8 Å. This material cannot be true perovskite (CaO.TiO₂) because the TiO₂ content of the cements is too small (Table 1). The structure of C₃A bears some resemblance to that of perovskite, being cubic with a cell-side four times that of the pseudo-cell of perovskite, and careful consideration of the intensities of reflexions suggests that these cements may contain little or no C₃A and that it has been replaced by a similar phase with the lower symmetry of perovskite.